Phosphate Homeostasis

Question 1

Role of phosphate in physiology

Answer 1

Bone mineral - calcium hydroxyapatite Ca10(PO4)6(OH)2
Nuclei acids
Phospholipids
ATP
cAMP
Post-translational modification of proteins

Question 2

Amount of whole body phosphate

Answer 2

500-800g
1% total body weight

Question 3

Serum phosphate amount

Answer 3

0.8-1.5 mmol/L

Question 4

What percentage of phosphate is found in bone mineral

Answer 4

90%

Question 5

Low phosphate

Answer 5

Poor bone mineralisation
-rickets or osteomalacia
-pain and fractures

Question 6

High phosphate

Answer 6

Excessive formation of hydroxyapatite
Deposition in tissues other than bone

Question 7

Dietary sources of phosphate

Answer 7

Protein:
Animal
Dairy
Soy
Seeds
Nuts

Question 8

Recommended daily intake of phosphate

Answer 8

700 mg

Question 9

What percentage of phosphate is reabsorbed in PCT of kidney

Answer 9

80%

Question 10

Renal phosphate handling

Answer 10

Maximum rate of reabsorption is limited
So excess is excreted

Question 11

How is phosphate reabsorbed in PCT

Answer 11

Na co-transporter

Question 12

How much phosphate is filtered in the glomerulus

Answer 12

90%

Question 13

How much phosphate is reabsorbed in the DCT

Answer 13

10%

Question 14

What hormones regulate phosphate

Answer 14

Parathyroid hormone
1,25 dihydroxyvitamin D
FGF-23

Question 15

Effect of parathyroid hormone on phosphate

Answer 15

Increases 1,25 vitamin D so increases active gut absorption
Decreases tubular reabsorption of phosphate- increases renal excretion

Question 16

FGF-23

Answer 16

Fibroblast growth factor 23

Question 17

What is the major regulator of phosphate metabolism,

Answer 17

FGF-23 (fibroblast growth factor 23)

Question 18

Where is FGF-23 produced

Answer 18

Osteocytes

Question 19

What stimulates the production of FGF-23

Answer 19

Rise in phosphate levels
Dietary phosphate loading
Parathyroid hormone
1,25 vitamin D

Question 20

Actions of FGF-23

Answer 20

Decreases expression of Na transporter in renal tubule- increases renal excretion
Decreases 1 alpha-hydroxylation of vitamin D- decrease gut absorption

Decreases whole body phosphate

Question 21

Secondary regulator of phosphate

Answer 21

Parathyroid hormone

Question 22

How is phosphate found in serum

Answer 22

50% free ions
35% complexed
10% protein bound

Question 23

What does phosphate complex with in blood serum

Answer 23

Na+
Ca2+
Mg2+

Question 24

What percentage of ingested phosphate is absorbed

Answer 24

70-80%